There is known a solid-fuel gasifying system, in which a waste such as waste plastic, sludge, shredder dust, municipal refuse, or a solid fuel such as coal is introduced into a thermal decomposition furnace. The solid fuel is thermally decomposed into a thermal decomposed gas or pyrolysis gas within a high-temperature reducing atmosphere of less or low oxygen concentration. A variety of combustion furnaces or incinerators may be generally used as a the thermal decomposition furnace, such as a waste gasification melting furnace, a coal gasification furnace, a rotary kiln type of thermal decomposition furnace, an external heating type of thermal decomposition furnace, a batch type of thermal decomposition furnace or a self-burning type of decomposition furnace and so forth.
The present inventors have recently developed a waste gasification system comprising a high-temperature air generator for continuously providing an amount of hot air at a high temperature exceeding 800 degree centigrande (referred to as “deg. C” hereinafter), and a waste gasification type of melting furnace containing a number of spherical ceramic balls, which is so-called “pebbles”. The high temperature air is introduced from the high-temperature air generator into the melting furnace, wherein the waste is melted and slagged on the spherical ceramic balls. Thermal decomposed gas or pyrolysis gas produced by thermal decomposition of waste is conducted out of the furnace and introduced into a gas treatment devices, such as a scrubbing devices and/or filtration equipments. The gas treatment devices remove various environmentally harmful substances, such as chloride, sulfur, heavy metal particles and unburned combustibles, from the thermal decomposed gas, and quickly cool down the thermal decomposed gas to avoid re-synthesis of dioxin. The thermal decomposed gas scrubbed, filtrated and cooled down is used as a relatively high-quality syngas to be fed to any of combustion facilities or heat engines, for example, a heating furnace such as a boiler or industrial furnace; an internal combustion engine such as a gas engine, gas turbine or diesel engine; or a variety of heat cycle systems.
As a current type of thermal decomposition gasification system, a system is known, which comprises a heat decomposition furnace for producing a quantity of thermal decomposed gas; a high-temperature gas treatment device such as a cracking device; and a gas scrubbing device for scrubbing and cooling the thermal decomposed gas. The thermal decomposition furnace functions to thermally decompose a liquid or solid fuel, such as waste or coal, under a low or less oxygen atmosphere of an internal combustion area in the furnace. The high-temperature gas treatment device cracks tar or oil contained in the thermal decomposed gas, and the gas scrubbing device is adapted to remove sulfur, dust, chloride and other harmful substances from the thermal decomposed gas while quickly cooling down the gas. Having taken such cracking and scrubbing treatments, the thermal decomposed gas is fed to a variety of combustion facilities as a cleaned up syngas.
In such a type of gasification system, a large amount of sensible heat of the thermal decomposed gas is lost in the scrubbing and cracking devices, so that the thermal efficiency of the whole system is degraded. In order to prevent such a heat loss, a steam reforming process is considered to be employed, in which steam is mixed with the thermal decomposed gas so as to reform the hydrocarbon in the thermal decomposed gas by means of a steam reforming reaction. Such a hydrocarbon steam reforming is, in general, an endothermic reaction which requires an amount of heat to be supplied to the area of reforming reaction by an external or internal combustion type of heating device.
The inventors have recently proposed an apparatus capable of continuously heating a quantity of steam up to a high temperature equal to or higher than 700 deg. C., which allows a study or research to be conducted with respect to applications of steam to be used as a high-temperature inert gas or a high-temperature heating medium. Particularly, as the high-temperature steam merely produces a quantity of water after its condensation, such an application of high-temperature steam is advantageous to simplification of treatment of residues after cooled down and condensed, which entirely differs from a case of use of the other inert gases such as nitrogen gas. In addition, the high-temperature steam at 700 deg. C. or higher, which possesses a large amount of sensible heat, acts to supply the reaction area with an amount of heat required for the reforming reaction at least partially.
However, it is found out that the heat of reaction required for the steam reforming reaction of the thermal decomposed gas cannot be sufficiently obtained even if the high-temperature steam exceeding 700 deg. C. is fed to the reaction area, and therefore, a simplified method or arrangement is desired to be developed, which can compensate for the shortage of heat required for the aforementioned reforming reaction.
Further, the present inventors has recognized a state in that the aforementioned waste gasification system may cause a relatively large quantity of soot to be produced within the furnace during the process of gasifying and melting the waste with the high-temperature air in a relatively oxygen-enriched condition. Thus, it is also desired to provide an approach which can efficiently restrict the generation or production of soot in the furnace.
Such being the case, the object of the present invention is to provide an apparatus and method for gasifying a liquid or solid fuel which can reform the thermal decomposed gas of a gasification furnace or thermal decomposition furnace so as to be a relatively high quality syngas.
Another object of the present invention is to provide an apparatus and method for gasifying a liquid or solid fuel which can ensure an amount of heat required for a steam reforming reaction of hydrocarbon in the thermal decomposed gas without provision of internal or external combustion type of heating devices.
Still another object of the present invention is to provide an apparatus and method for gasifying a liquid or solid fuel which can promote or urge the thermal decomposition and gasification of the fuel in a gasification furnace or thermal decomposition furnace while restricting production of soot in the thermal decomposition area.